Antibodies specific to histones, non-histone chromosomal proteins HMG-1, HMG-2 and HMG-17 and to nucleosomes have been used to study the structure-function relation of defined chromosomal components in chromatin and chromosomes. A sensitive solid-phase radioimmune assay for chromosomal components has been developed. The interaction of IgG molecules with the chromatin subunit has been studied by the interactive computer graphics technique. The antibody molecule cannot interpenetrate between adjacent DNA strands to reach determinants in the histone regions covered by DNA. The complexing of chromosomal proteins into the nucleosomal conformation brings about conformational changes or steric hindrance so that part of the antigenic sites are masked. Nucleosomes elicit antibodies directed against determinants which are nucleoproteins composed of DNA and the N-terminal segments of the histones. Specific antibodies have been microinjected into oocytes of Pleurodeles waltlii. Antibodies to histones bring about a specific retraction of the transcriptional loops in the lampbrush chromosomes present in these oocytes.